At present, there are two known methods for cultivating bacteria and their metabolites. These methods are generally described as batch and continuous cultivating.
A suitable liquid medium for cultivation should contain a nitrogen source (pepton or trypton), necessary growing factors (autolized yeast or yeast extract), and a carbon source, suitably glucose or lactose. If desired, a suitable base can be used as a pH-stabilizer. Generally, all such solutions should be autoclaved in accordance with the substratum manufacturer's instructions. However, if ammonia is used as a base, this should first be sterile filtrated.
A specific cultivating medium may, for example, have the following composition: 10 g trypton or pepton (Oxoide or Difco); 3 g yeast extract (Oxoide or Difco); 20 g glucose or lactose, purum or puriss (the quantities are stated per liter of cultivating medium). Generally, pH-adjustment can be made with 0.5 M NaOH or NH.sub.3 to 6.2-7.0, and preferably to 6.5. Typical temperatures for cultivating are from about 28.degree. to 35.degree. C, and preferably 31.degree. C.
Cultivation according to the prior art techniques was accomplished in the case of a strain of Streptococcus faecium, specifically S.faecium M74 utilizing the aforementioned cultivating medium and by means of adjusting units (pH and temperature) in a 10 liter BIOTEC-fermentor. The strain S.faecium M74 is deposited at the National Collection of Industrial Bacteria, Torry Research Station, Aberdeen, Scotland, with the number NCIB 1181 and has been given the code name S.faecium M74. Generation time for S.faecium M74 is approximately 20 minutes under the above-mentioned conditions. Under such conditions, a fully grown medium will contain approximately 10.sup.10 V.C./ml S.faecium M74 organisms after 5 hours. One hundred milliliters of a 12-hour-culture of S.faecium M74 in the same medium as above, but without pH-adjustment, yields a cell quantity of approximately 10.sup.8 V.C./ml.
As noted above, this cultivating method can be applied to batch cultivating as well as continuous cultivating. When cultivating the investigated S.faecium M74 strain continuously, it was found that the maximum diluting rate was 0.5/h under the above-mentioned conditions. Large-scaled tests confirmed, however, that yet a third cultivating method was to be preferred. This cultivating method, which is known as pulsatory cultivation, is the subject of the present invention.